This invention relates in general to control systems for vehicles and more specifically to vehicle mass estimation techniques.
The determination of vehicle mass is important to the efficient operation of today""s vehicles, especially in the heavy-duty commercial and industrial truck industries. For example, mass can be a selection criteria for proper gear changing control in a transmission having staged gears. Vehicle mass may also be used by various vehicle controllers in anti-lock brake systems, intelligent vehicle/highway systems and fleet management systems, to name a few. In addition, vehicle mass can be useful in speed control systems, such as for use with a cruise control system. One problem with using vehicle mass as a control parameter is that it varies with vehicle loading and is usually difficult to predict with certainty, especially with respect to heavy-duty trucks. For example, a dump truck can have a mass when loaded up to ten tons greater than when empty. In the case of a semi-tractor with a trailer, the mass when loaded can be up to 40 tons greater than when empty.
Because the mass of a particular vehicle may vary greatly, a means for accurately measuring actual vehicle mass when the vehicle is in operation is required if the dynamic vehicle mass is to be used as a control parameter. Thus, if the mass parameter is fixed at a particular value in the control system, then the various control features described above will not allow for optimal vehicle performance under all types of load conditions.
Various methods of measuring vehicle mass have been the subject of prior patents. In U.S. Pat. No. 5,490,063 to Genise, a method for determining vehicle mass as a function of engine output or driveline torque, vehicle acceleration, and the currently engaged gear ratio is disclosed. For this method, Newton""s law is used directly with acceleration and force values determined from the torque and gear ratio input to estimate vehicle mass. Likewise, in U.S. Pat. No. 4,548,1079 to Klatt, a method is disclosed for determining vehicle mass directly using engine output torque values and acceleration values.
Vehicle acceleration is typically computed from either engine or vehicle speed data. However, one of the problems associated with the collection of speed data is that speed signal is typically very noisy. When vehicle acceleration is used to determine the vehicle mass, the noise problem is even more significant. In order to determine acceleration, it is often necessary to measure the increase or decrease in speed values at very close time intervals. This differentiation in speed values at close time intervals causes the acceleration signal to be buried in the noise of the speed signal. Inaccurate determinations of vehicle acceleration and a correspondingly inaccurate determination of vehicle mass may result. The various controllers relying on an accurate vehicle mass determination may in turn perform ineffectively and inefficiently.
What is therefore needed is a technique for estimating vehicle mass that addresses the foregoing shortcomings. Such a technique should provide reliable, accurate estimates of vehicle mass. The method should also effectively address the problems created by the inherent noise contained in speed signal data. The technique should also be inexpensive to implement, and be readily integratable into existing vehicle control systems.
The present invention addresses the foregoing shortcomings in estimating vehicle mass. In accordance with the present invention, a technique for processing vehicle speed signal data and vehicle push force data to estimate vehicle mass is disclosed. The technique results in an accurate and reliable estimate of vehicle mass and/or aerodynamic coefficient. The technique also minimizes the effects of speed signal noise in the computation of vehicle mass.
In accordance with one aspect of the present invention, a method is disclosed for estimating the mass of a vehicle that has an internal combustion engine producing a torque in accordance with a fueling rate provided by a fueling system thereof. The torque is applied to a drive-train coupled to the engine. The drive train includes a transmission coupled to the engine that has a plurality of engageable gear ratios, a drive axle, and a propeller shaft coupling the drive axle to the transmission. The drive axle has at least one wheel for moving the vehicle. This method includes: (a) continually determining a vehicle speed and a vehicle push force corresponding to the vehicle speed and storing corresponding vehicle speed and vehicle push force data within a memory portion of a control computer; (b) qualifying a segment of the vehicle speed and push force data; and (c) determining vehicle mass by a recursive least square estimation analysis of the qualified segment of data by defining the vehicle speed as a function of the push force. A vehicle aerodynamic coefficient may also be determined.
In another aspect of the invention, the determination of vehicle speed and push force includes determining a shift status. Additionally, the qualification of the data segment may include buffering the vehicle speed, push force, and shift status data, and selecting the longest qualified segment therefrom. The invention may further include correcting the estimated vehicle mass and aerodynamic coefficient when one of the estimates falls outside an upper or lower limit.
In a further aspect, a control system for a vehicle is disclosed for estimating mass of the vehicle. The control system includes an engine with a fueling system associated therewith, a transmission coupled to the engine having a plurality of engageable gear ratios, a drive axle, and a propeller shaft coupling the transmission to the drive axle. The system further has means for determining a vehicle speed and providing a vehicle speed signal corresponding thereto; means for determining an engine fueling rate and providing an engine fueling rate signal corresponding thereto; means for determining a presently engaged gear ratio of the transmission and providing a gear ratio signal corresponding thereto; and a processor responsive to the engine fueling rate signal and the gear ratio signal to determine a vehicle push force corresponding to the vehicle speed signal. The processor is further responsive to qualify a data segment from these signals and calculate an estimated vehicle mass by a recursive analysis of the qualified data segment, where the vehicle speed is expressed as a function of push force.
In another aspect of the present invention, the control system further includes a data communications link connected to the processor, with the engine percentage torque, the vehicle speed signal, the gear ratio signal, or the gear engagement signal being provided to the processor from a remote processor via the data communications link.
It is one object of the present invention to provide a technique for filtering and qualifying speed signal data and push force data so it may be used to accurately estimate vehicle mass.
It is another object of the present invention to provide a technique for recursively analyzing speed and push force data to estimate vehicle mass and/or aerodynamic coefficient which minimizes effects of external factors and the error associated with estimates based on little data.
Another object of the present invention is to provide a mass and/or vehicle aerodynamic coefficient estimation technique that is readily integratable into existing control systems.
It is yet another object of the present invention to optimize the performance and efficiency of vehicle systems and components by providing accurate estimates of vehicle mass and/or aerodynamic coefficient.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.